1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to separation devices for removing an image bearing sheet from an image carrier in an image forming apparatus.
2. Description of the Related Art
Conventionally, in a typical image forming apparatus, electrostatic copiers, a transfer charger and a separation charger are arranged around a photosensitive body. After transferring a developed image from the photosensitive body onto a copy sheet while the copy sheet is in contact with the photosensitive body by action of the transfer charger, the copy sheet is separated from the photosensitive body by action of the separation charger. However, occasionally the copy sheet cannot be separated completely from the photosensitive body because an insufficient charge is applied by the separation charger to the copy sheet. In this case, the non-separated copy sheet unfortunately can infiltrate into a cleaning device and cause a jam. For preventing the above-mentioned problem, conventionally, a separating claw is arranged against the photosensitive body to physically remove the copy sheet before the sheet reaches the cleaning device.
For the separating claw which constitutes this type of separation device, usually a hard plastic, such as ABS resin or Delrin (a trade name of Du Pont Co. for an acetal resin), and an elastic film, such as Mylar (a trade name of Du Pont Co. for a polyester film) have been used. By causing the sharp tip of the separating claw to make contact with the surface of the photosensitive body at an appropriate time, the copy sheet can be separated from the photosensitive body after passing the transfer charger and separation charger. The separating claw provides an auxiliary mechanism to prevent the copy sheet from entering the cleaning device and causing a jam.
However, in the above conventional separating claw, and particularly in one made of a plastic such as ABS resin, the hardness often is too high. For this reason, the surface of the photosensitive body, which normally is formed of a comparatively soft material like selenium (Se), can be easily damaged by this contact with the photosensitive body. Therefore, problems occur in that the picture quality of the developed image may become poor.
In order to compensate for the above problems, a soft film such as Mylar has been used for the separating claw. When Mylar is used, there has to be a complex construction in which a harder material is used as a base member, in order to maintain the accuracy and configuration of the Mylar portion, which makes contact with the photosensitive body. Accordingly, construction of the separation claw becomes complex, more expensive and time consuming. In addition, the surface of the photosensitive body may be easily damaged by contact with the harder portions of the separating claw construction. Another problem, which sometimes arises, relates to the electrostatic attraction of the copy sheet to the photosensitive body. If the contact pressure of the claw on the surface of the photosensitive body is too low, the copy sheet may more easily enter the cleaning device without separating from the photosensitive body. Thus a breakdown of the cleaning device or the apparatus may result.